It's a weak argument because we have entered a fundamentally different phase of our evolution, from that steered by our environment to that steered by ourselves. Our evolutionary drives incite us to eat meat because it was scarce (but now we have farms), they incite us to view faces different than ours as fundamentally other (though tribalism is obsolete and we recognize everyone as human). There is no good reason to follow evolutionary imperatives because we now understand our own impact on our destiny and have the means to plan for and steer it.

It is the weakest because there are only a few good arguments for life extension, and all of them are better (but not by much) except for the "because we can" people.

Always when introducing these "benefits" to society we must carefully weigh and consider the way they will shape how human lives are led and experienced. And nothing good can come of extending life if there is no corresponding marked increase in quality of life for everyone who may be affected--and I don't just mean statistics like access to healthcare and food, but real, perceived happiness of individuals.

Quick edit to respond to your last point: "truths" in this context hardly mean much. There are very few things you can call objectively true. There are metrics and statistics you can measure but they only explain themselves and any correlations you may assign are spurious at best, and harmful when acted upon without fore- or afterthought.